Apparatus for making cement by the wet process



T. RIGBY March 26, 1929.

APPARATUS FOR MAKING CEMENT BY THE WET PRO CESS Filed Dec. 8. 1922 2Sheets-Sheet March 26,1929. 11mm 1,706,747

APPARATUS FOR MAKING CEMENT BY THE WET PROCESS Filed Dec. 192 2Sheets-Sheet 2 Patented Mar. 26, 1929.

UNITED STATES- THOMAS BIGBY, OF

LONDON, ENGLAND.

APPARATUS FOR MAKING CEMENT BY THE WET PROCESS.

Application filed December 8, 1922, Serial No. 605,680, and in GreatBritain December 19, 1921.

v This invention relates to the manufacture of cement (especially inplants of the rotary kiln type) and has particularly for its objects tosecure economy of fuel used n the drying of the materials and theburning of the cement. p

This the invention achieves by effecting drying outside the kiln in aparticular way, and by the heat of gases discharged from the kiln, ofmaterial to be made into cement.

' The said particular way of carrying out this drying consists indispersing the material in a rapidly moving current-of thehot gases sothat the same is held in suspension by the gases as they are drying it.p

- The invention may in its application under difierent circumstancestake widely differing forms and before proceeding to a consideraby thedry method.

tion of some of these varieties and their advantages it will beconvenient to describe in detail andlwith reference to the accompanyingdrawings a plant which may be regarded as one example of plant accordingto the invention. i

This illustrative plant is constructed and arranged for dealing withcement slurry that is to .say it is one intended'for employmentwhere theinvention is applied to cement making by the wet method and wheretherefore a semi-fluid slurry containing say some of water and all theingredients for making the cement is to be dried according to theinvention. It should, however, be pointed out that the invention isnotconfined to cement making by the wet method since thegas'esdischarged from a so-called dry kiln are am ply hot enough even whencooled under steamraisingboilers (as is sometimes done atthe presenttim-e) to be used as drying medium in theparticular way aforementionedfor removing excessive moisture from an individual v material of thoseto be mingled together in the apparently dry condition for discharge inthis condition into the kiln in cement making In the accompanyingdrawings which are to be regarded as purely diagrammatic (and in whichin the interests of ready understanding details of plant constructionmaking for efliciency and obvious to those skilled in the arts of dryingmaterials and conveying gases, such as the introduction of one gascurrent into another by a duct discharging into another at a small acuteangle in the direction of flow of the mingled cur ents rather thanperpendicularly or at a large angle are omitted).

Figure 1 is a general elevation of the plant;

Figure 2 shows an arrangement for controlling the discharge of slurryinto the current of gases;

Figure 3. is a plan indicative of a convenient way of spreading theslurry on the drying surfaces of film drying apparatus by which in theillustrative plant the apparatus for dryinglthe material in suspensionin a gas current is shown as supplemented, and

Figure 4 is a detail enlarged side elevation, partly in section, of thecentral portion of the plant as shown in Figure 1;

Figure 5 is an enlarged View, partly in section, of the right handportion of the tube shown in Figure 4.

In the plant shown hot gases discharged from the rota" y kiln 3 into theflue 5 can be drawn bya fan 7 through a control damper 9 and duct 11into a drying duct composed of a rising portion (comprising parts 13 and15 hereinafter referred to) and a portion 17 of any convenientdisposition and length connecting the top of the rising portion and thefan. The slurry is discharged into the gas current at the bottom of therising portion of the duct and the particular devices shown in thisinstance for this purpose comprise a spraying jet 19 (see also Figure 2)located in a hood 21 preferably suitably insulated having an opening 23above, and coaxial with, the jet. The hood is situated in a downwardextension 25 of what has been referred to as the rising portion of thedrying duct so that both it and the jet within it are out of thedirecthot gas current discharged by the duct 11. The hood acts to shieldthe jet from the hot gas and to trap on its inner surface such ortion ofthe material dischargedfrom the et as would otherwise fail to be takenup by the gas current and be apt to be deposited on the wall ofthe'drying duct and accumulate thereon or fall back in a partly driedandobthe bottom of the extension25 which is sealed by dipping in thesupply of slurry. Provision is made for adjusting, by any convementmeans, the relative heights of the jet 19 and hood 21 so that the lattermay be employed to control the spread of the jet of slurry and the rateof admissionof slurry into the gas current. vThese latter functions ofthe hood will become apparent from Figure '2 which shows how thedistance of the jet 19 from the opening 2'3 alfects the contained angleof the jet of slurry and the proportion of the jet of slurry which isactually discharged into the current ofgases.

WVhile the material is still moist it is apt to cohere and is prone todeposit on and build up on the Walls of the duct if perchance it touchesthe same andit is to reduce the like lihood of this latter occurrencethat the slurry is preferably introduced into the gas current in, asshown, a substantially vertical section of the duct. In addition it ispreferable so to correlate the temperature of the gas current meetingthe slurry, the velocity of that current and the amount of slurrydischarged into the current that before the current su-ffers a markedchange in direction inducing deposition (that is in this case before thetop of the vertical section of duct is reached) the material shall havebeen dried beyond the condition in which it is still apt to adhere tothe duct walls. While different conditions would dictate widely varyingproportions of drying duct it may here beconvenient to indicate that afirst vertical section'13 and 15 of some 40 feet in length of atotal-length of drying tube of say 150 to 200 feet would be in no senseout of the range of conyenient and likely sizes. To guard againstaccumulation of deposit in the vertical section of the duct it ispreferable to provide cleansing devices and convenient forms areindicated in the drawing. For this purpose the section 13 through whichthe material passes in its wettest state is preferably made rotatable)being say.

driven by a pinion on a power shaft 37 and engaging a pinion 39 fast onthe section 130 and supported on the'extension 25 by means of a ballbearing 14. Guide rollers 12 mounted in brackets 16 carried by anysuitable part of the plant are provided to maintain section 13 inposition transversely. In the interior of the section 13 is a stationaryscraper 41, which is fixed at its lower end to a lug 40 on the insideofthe extension 25. The upper end of the scraper 41 is fixed to a lug 42which projects downwardly-from a ring 18 on the interior of anenlargement 20 of the stationary section 15. Thus any tacky materialwhich may become deposited on the wall of the section 13 is scraped offby said scraper and drops back into the slurry tank. Where the materialis drier in the upper portion 15 of the vertical section of the duct andmore likely to behave as a solid when scraped oif and'to be in acondition favouring'its being carried forward by the gases, it ispreferable to use in this portion a'group of rotary scrapers placed asmall distance apart peripherally of the duct. To this end a group ofscraper bars 43 extending longitudinally of the tube between endrings44, 46 are conveniently provided and are causedto rotate ax ially of theduct within the stationary section 15, as by a pinion fast on a shaft 47and engaging a pinion 49 fast on the upper end ring 46. The lower endring 44 is supported on the ring 18 by means of a ball bearing 22,

r and the upper end ring 46 is rotatably mounted on a flange 48 on thesection 15 by means of a ball bearing 50. 'A ball bearing 52 is alsointerposed between the end ring 46 and a flange 54 on the upper part ofthe duct. The stationary section 15 is maintained in position bybrackets 56, and the end ring 44 is guided transversely by means ofrollers 58' mounted in lugs 60 provided on the interior face of theenlargement 20 of the section 15.

'Where the gas current suffers a marked change of direction at the upperpart of the rising section of the duct and the suspended materialtending to retain its direction of motion is impelled towards the marginof the current of gases there is preferably provided a device whichensures that if for some reason the material is still apt to deposit onthe walls of the duct accumulation of such deposit will be prevented andin the construction illustrated this takes the form of an endless bandor belt 51 passingover pulleys 53, 55 and forming in effect the wall ofthe tube on which the outer portions of the gas current impinge as thelatter sweeps round the bend pulleys in a direction to bring any depositupon it over the duct 17 into-which the deposit drops, to be borne awayby the gas current, as it is scraped off the band by a scraper 57 pastwhich the band travels and which is kept pressed-against the latter, asby a weight 59, it being understood that the higher 'into the duct 17.The band is driven by the the slurry dried, it may be, to contain something under 10% of water is deposited and from which it is fed byconveying-means 63to the inlet chute 65 of the kiln after beingconsolidated, if this is desired, by any suitable form of briquettingdevice such as a rotary press forming avoid briquettes and indicated at67 or being slightly moistened to cause it to cohere and avoid to greatan expulsionof the material as dust from the kiln by the gases leavingthe same. Where the moisture content of the material deposited in thecyclone separators is substantially greater than that just referred to,stirring or conveying means may be necessary in the separators to avoidclogging therein.

As the volume of hot gases available from the duct 11 will notordinarily suliice for the convenient transport, to dry the same insuspension, of that quantity of slurry which it is desired 'to dry insuspension it' is generally desirable to augment this volume either byaddition of air or by returning to the'drying duct a portion (and maybethe bulk) of the gases after the separation of dried material therefromor in both these ways and it is for this reason that the duct 69 leadingthe gases from the cyclone separators is branched so as to lead by abranch 71 (in which is a control damper 73) to a washing tower 75 and bya branch 77 (in which is a control damper 79) to the duct 11 and thatthere is an air inlet 81- (controlled by a damper 83) to the branch 77.The washing towel through which such part of the drying current as isfinally rejected passes to the chim:

ney 85 is furnished with spraying devices 87 which may be supplied withslurry (instead of water which would militate against the eco-. nomicalrecovery of the dust) through a pipe 89 by a pump 91 fed from a slurrytank 93 thewashings in such an event being conveniently diverted througha pipe 95 to the tank 27 so' that the slurry which has in washing thegases been enriched (by the dust extracted from these and, if the gasesreaching the tower through the branch 71 are still at a temperaturesubstantially above their dew point, also possibly enriched by actualevaporation of water therefrom in performing the gas washing) is addedto the slurry supply for the jet 19.

lVhile the maintenance of thetemperature of the gases reaching thewashing device at a temperature suiliciently above their dew point willavoid=dilution of the slurry by con- (lcnsation (and may as pointed outabove even result in concentration of the slurry) such deposition mayalternatively be guarded against by warming the slurry to be used in gaswashing.

'As willmore clearly appear from the discussion hereinafter of thedifferent circumstances likely to be met with and the.variations ofplant which the attainment of highest fuel economy may favour in variouscircumstances it will sometimes be advantageous to associate a differentform of drying plant with an installation such as has been so fardescribed with reference to the drawings and which installation is onthe other hand a complete entity and will often be preferred in thisform on account of its low capital cost and general simplicity even atthe sacrifice of some economy of fuel. Such an associated plant is shownin the drawings and takes'the form of a high economy steam-heated filmdrier. Two such driers are indicated at 100, 102 and may derive theirheating steam directly from boilers heated by the kiln gases or from theexhaust of steam driven primemovers supplying power for the cement worksand heated it may be by steam generated by the heat of the kiln gases.Again a plurality of such driers may operate independently or inmultiple-effect.

Steam for such a purpose may be derived from a boiler 104 heated bygases drawn from the flue 5 by a fan 106 which discharges the gasesthrough a chimney 108, there being a control damper 110 in the duct 112connecta ing thefan and the boiler flue and there being also if desireda connection controlled by a damper (indicated respectively at 114 and116) between the ducts 112 and 11 so that gases from the boiler flueinstead of directly from the flue 5 may be drawn through the drying tubeby the fan 7. At 118 is, indicated an engine, say supplying power forthe cement works, which may be furnished with its steam wholly or inpart from the boiler 104 and the exhaust'from which instead of passingdirectly to the condenser 1 20 may wholly or in part be diverted bymeans of the valve 122 into the film driers through the duct 124 to heatthe same and the steam generated in these (or in the low temperature onethereof if by closing certain of the valves shown and opening others thedriers are employed in multiple-effect rather than as independent.assumed to be spread thereon by smaller drums 127 having a peripheralspeed differing from that of the larger drums, the slurry being suppliedto the bite of the drum pair from a slurry conduit 131 formed by abridge piece 29 and these conduits being supplied through ducts 133 withthe slurry from the tank 93 by means of a pump135. At 137 is indicated aconveyor which receives the dry material from the driers 100, 102,through the ducts 139, 141, and delivers it directly to the chute 65 orto the briquctting device 67. if one be used.

Such a connection as 114 may be convenient in allowing the drying ducttobe supplied with gases from the boiler flue during periods when there isa considerable call for power and to be supplied with gases directlyfrom the kiln at times (such as week-ends) when the power needs of theplant, for mixing, crushing and soforth, are largely cutv down.

The details of construction of such film drying apparatus as lastreferred to have not tors Patent No. 180963 for constructional 1features which it is preferred to employ in the interests of efliciencyin film drying apparatus used in carrying out the present invention. I

Having considered in detail one form of the invention it nowbecomespossible to appreciate more readily the advantages possessgas currentand its continued suspensionv ed by the process of drying the materialin suspension in a current of hot kiln exit gas before the material isintroduced into the kiln-a process which actually turns to usefulaccount that transporting capacity of't he kiln gasses which has alwaysbeen regarded by the cement manufacturer of today as troublesome andcostly in impossing upon him theneed of equipping the kiln with dustcatching devices to cleanse the kiln gases of cement and cementmaterials dust in order to avoid nuisance and loss. If one regards theproblem of fuel economy in cement making as dependent upon onesability-todischarge the kiln gases from the system only after they havebeen cooled, in effecting useful heating in cement making, to a lowtemperature it becomes apparent how advantageous the process in questionis since the gases may be discharged from .the drying duct just abovesaturation point at a temperature of say 80 deg. C.-a degree of ofcooling, as the result of drying action, which is unattainable inpractice by any other drying process. Moreover since gases at quite alow temperature say as low as 200 deg. C.

.may usefully be employed as the drying .medium in such a process itfollows that even gases cooled after leaving the kiln by raising steamin a boiler do not need to be rejected from the system then but can dostill further useful work-as has been indicated.

These results flow, manifestly, from the intimacy of contact between andthe resulting quick and complete heat transfer of heat between the gasesand the material to be dried which the dispersal of the material in thetherein admit of.

The employment of such a process in making cement by the wet methodmarkedly increases the cement output possible with a given kiln and inthe case of complete drying of the slurry before it enters the kiln theduties of the latter become exclusively be shown in this way that (a)when using merely a drying duct in which the slurry is dried asindicated in suspension in the kiln gasses and in which the heat of thegases (leaving-the kiln under these conditions at some 600-800 deg. C.rather than the more customary 400 deg. C. which occurs when the kilnhas to perform the drying) is reduced in temperature by drying to some8.0 deg. C., a fuel economy of some 33% should be expected; (6) whenusing in the drying duct kiln gases already cooled in raising steam toprovide part of the factory power and furnish exhaust steamfor a filmdrier (for part of the slurry) interposed asv described, between theprime mover and the condenser an overall fuel economy of some 60% shouldbe expected; and (0) when using in a combination of film and suspensiondrying as last described steam for the power plant (which provides theexhaust steam for the film drier) which is generated otherwise than bythe heat of the kiln-gases and using these latter for the suspensiondrying at a kiln exit temperature of say 600 deg. 0., a fuel economy ofsome 50% should be expected.

While preferably the process will be so conducted that by the control ofthe rate of admission of slurry to the gas current (which it may bepointed out may reach a velocity of 60-70 feet per second or upwards inthe drying duct) it will be assured that the gases are finally rejectedin a nearly saturated condition at a temperature of some 80 deg. C andthe slurry'will be practically dry when the process is-working normallyyet it should be understood that the process is susceptible of manyvariations since the drying of cement material by suspension in acurrent of hot kiln gases may, to give instances, be advantageouslyadopted to effect the drying in but a comparatively short duct, andconsequently by but a partial cooling of the gases, of only a smallproportion of the material or the drying of a larger proportion to alesser degree or adopted to dry further a quantity of slurry partlydried on a high heat economy film drier or adopted to dry material byexposing one batch thereof to the current at a relatively hightemperature and another batchthereof to the same current at a lowertemperature after the first b'atch dried there by has been separatedtherefrom.

It will be understood that, without departing from the-invention,methods and devices differing Widely from those above described may beadopted for dispersing in the current .be preferable to disperse thematerial in a current of gas, such as air or circulated gases suppliescorresponding to those supplied in the example fully described abovethrough the ducts 7 7 and 81 respectively, which only becomes heated andan active drying current after it has travelled so far from the locationat which it received the dispersed material that that portion of thematerial which it does not readily transport shall-have been dropped byit under conditions which are not so likely to cause difficulties asthose presented by the dispersal of the material into hot gases which byheating the duct walls and exerting an immediate drying action on thematerial thrown into the current require that special measures, such ashave been described with reference to thedrawings, be taken to avoidcaking of the material on the duct Walls and the formation of lumps andmasses of semi-driedmaterial from that portion which is not carriedspeedily away by the current. In dealing with cement slurry it is to beobserved that the smoother the duct walls the less prone is the spray tostick thereon when it strikes the same and, for example, the

enamelling of the duct walls may therefore be considered advantageous.

Moreover, while in the example described the drying duct has beenconsidered] -as equipped only at the first bend and in the course of itslength to that bend respectively with a band or like device toreintroduce deposited material into the gas current and with .ductscraping means it should be pointed out that such devices may be used,as the case may be, at any other bend or length of the duct and itshould further be pointed out that such duct scraping means may bereplaced or supplemented by other forms of device such as duct hammeringor vibrating means acting to detach deposit from the duct walls.

While reference has been made above to the use of cyclone dustseparators as means for separating the bulk of the dried material fromthe drying gases and of washing devices for removing thereafter furtherquantities not recoverable by such dust separators it should bepointed'out that other forms of depositing chambers or else dust filtersmay take the place of the cyclone dust separators or that such filtersmay be. used as auxiliaries to such separators or to other formsofdepositing chamber to trap residual dust in the gases it being worthyof. note that the low temperatures to which these gases can be andusually are brought in this method of drying admit of the use of hi hlyefiicient filtering cloths or the like whic may be unutilizable incurrent practice owing to the destructive action of the high temperatureof the kiln exit ases.

g Again cyclone dust separators or other depositing chambers may be usedin series so as to free the gases step by step to a greater andgreaterdegree from suspended dust and reduce the duty on the ultimatewashing or filtering devices if such remain necessary. Customarily theclinker leaving the cement kiln is cooled in heating air which is tosupport combustion in the kiln furnace, and while the clinker may incarrying out the present invention be cooled instead by air which isthus heated to fit it for use as drying medium in the drying duct, yetit may occur in carrying out this invention that the economy in fueconsumption bringswith it such a reduction in the heat which canusefully be, or needs to be, abstracted from the clinker by amorelimited quantity of air needed for burning the lesser quantit of fuelthat an extra quantity of air can be eated in cooling the clinker andthis excess diverted to. the; drying duct to supplement the kiln gasestherein. Even more advantageous is it to abstract any such excess ofheat from the clinker by gases from the drying duct which, having hadthe dried suspended material removed therefrom to the highest degreewhich the plant admits of, are heated by the clinker and used anew asdrying medium in the duct since in this case heat of the clinker is notuselessly consumed in heating up gas from atmospheric temperature to atemperature well above the same and yet below which it cannot be cooledby drying action.

I claim 1. In an apparatus for making cement by the wet process, anup-right tube for drying slurry connected adjacent its lower end to agas exit of a cement kiln and at its other end to a centrifugal dustseparator and collector, a slurry spraying device at the lower end ofthe drying tube, a scraping member bearing against the inner wall ofsaid tube for removing the slurry, and means for rotating said scrapingmember.

2. In an apparatus for making cement by the wet process, an up-righttube for drying slurry connected near its lower end to a gas exit of a"cement kiln and at its other end to a centrifugal dust separatoriandcollector, a

to detach the slurry collected thereon, and

means for movingthe endless band. 7

3. In an apparatus for making cement by the wetprocess, a slurr -dryingtube having two vertical parallel llmbs joined'at their upper ends by abend and whereby one limb is connected near its lower end to a gas exitof a cement kiln while the othei' limb is connected to a centrifugaldust separator and collector, a slurry spraying device at the 5 lowerend of the first-mentioned limb of the drying tube, a moving endlessband mounted in said bend and extending thereacross so as to be engagedby the gas stream containing the slurry, ascraper arranged at the upperend of the second-mentioned limb to detach 10 the slurry collected onthe moving band, and

means for moving said endless band. In testimony whereof I aflix mysignature.

THOMAS RIGBY.

